Single core magnetic voltage regulator



Dec. 15, 1970 5. WEDEMEYER 3,548,292

SINGLE GORE MAGNETIC VOLTAGE REGULATOR Filed Dec. 20, 19s? 's Sheets-Sheet 1 PRIOR ART Mam 02 III PRIOR ART 2 Fl 6. 2

' BNVENTOR Ger mm W V BY lac/mug 5'. 3AM

ATTORNEY D06. 15, 1970 WEDEMEYER 3,548,292

SINGLE CORE MAGNETIC VOLTAGE REGULATOR Filed Dec. 20, 1967' I 5 Sheets-Sheet 2 PRIOR Am 5 A Mifn/aIK III 2 PRIOR ART ump PRIOR AR] ATTORNEY n. 15, 1970 WEDEMEYER 3,548,292

SINGLE CORE MAGNETIC VOLTAGE REGULATOR Filed Dec; 20. 1967 s Sheets-Sheet s I I I 'I 9/ FIG. .9

ATTORNEY United States Patent 3,548,292 SINGLE CORE MAGNETIC VOLTAGE REGULATOR Gerhard Wedemeyer, Brilon-Gudenhagen, Germany, as-

signor to Dominitwerke Gesellschaft mit beschrankter Haftung, Brilon, Westphalia, Germany Filed Dec 20, 1967, Ser. No. 692,094 Claims priority, application Germany, Dec. 24, 1966, D 51,882 Int. Cl. Gf 3/06; H01f 21/08; H02m 5/12 U.S. Cl. 323-61 3 Claims ABSTRACT OF THE DISCLOSURE Current surges upon switching-in of the voltage regulator are decreased and the regulatory region of the voltage regulator is increased by first, providing an additional path for primary leakage induction and secondly, shortening the length of the primary leakage flux lines. The former is accomplished by an additional section either by increasing the length of the coil over the height of the core or by arranging the compensation winding underneath the primary winding, so that the volume occupied by the compensation winding is available for absorbtion of additional primary flux. The path of the lines are shortened by filling the additional cross-sectional volume with magnetically conducting material.

BACKGROUND OF THE INVENTION The invention relates to magnetic voltage regulators. In particular it relates to magnetic voltage regulators having a primary leakage path and a capacitance which is connected in parallel with the secondary winding. It is the object of the present invention to increase the range of regulation of the conventional voltage regulator arrangements, that is, to increase the region within which the input voltage may vary without having the output voltage exceed the usual tolerances.

Furthermore, the current surges which appear when the voltage regulator is switched in, and which reach their maximum value when the switching occurs at the time the applied voltage passes through zero, are to be reduced to levels which will not damage the other equipment.

Conventional voltage regulators of the magnetic type consist of the combination of an unsaturated air gap inductance and a highly saturated transformer which is so strongly magnetized by a condenser which is connected in parallel with it, that its output voltage is the voltage corresponding to the saturation induction of its core, independent of the magnitude of the input circuit voltage. The output voltage of the output regulator is therefore approximately constant and independent of the input voltage over a Wide region. On the other hand, the constant voltage which is so obtained has a considerable number of odd harmonics superimposed upon it, because of the high saturation of the iron. It therefore has an output voltage curve which is substantially trapezoidal. This is suitable for subsequent rectification.

However, for other applications, a more or less sinusoidal output voltage may be required. This may be obtained by additional filters which reduce the harmonics to the desired level.

Other magnetic'voltage regulators with either trapezoidal or sinusoidal output voltages are known in which transformer are incorporated in one core as shown f.i. in FIGS. 1 and 3 whereby the core cam consists of several single cores and their combination. The arrangement according to FIG. 1 yields a substantially trapezoidal, the

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arrangement according to FIG. 3 a substantially sinusoidal output voltage.

The operation of these conventional arrangements may be described with reference to FIGS. 1 through 5.

The voltage regulator having a trapezoidal output voltage consists, as shown in FIG. 1, of a core, on which the primary winding 2 and the main winding 3 are decoupled by a magnetic shunt 4 which contains an air gap 5. Thus the flux associated with the windings 2 and 3, respectively may assume very differing values, allowing the voltage per turn of the two coils to diifer one from another. This is the basic assumption for constant voltage in winding 3 under varying circuit voltages in winding 2.

FIG. 2 shows the connections of the individual windings of the voltage regulator.

Even when a relativley small input voltage is applied to winding 2, an at first also relatively small voltage is generated in winding 3, which causes the capacitor 6, which is connected in parallel with the winding 3, to be charged. The capacitor then accepts capacitive energy and returns magnetic energy to the winding 3. This magnetization energy increases the flux which is linked with winding 3 and thus in turn the voltage on the winding 3. The charge on the capacitor is thus increased and it thus again returns magnetizign energy to the winding 3, etc.

When the capacity of the capacitor is sufiiciently high, this interchange continues in an almost avalanche form until the flux linked to winding 3 is saturated. This prevents the voltage which is induced by the saturation flux from increasing further. No increase is possible even if the voltage applied to the primary winding increases.

Thus, the voltage regulating characteristic of the voltage regulator is generated by the magnetizing effect of the capacitor, which drives the flux linking through certainly not sinusoidal voltage. Due to the saturation characteristic of the flux, the voltage in winding 3 is approximately trapezoidal, that is, it contains a high percentage of odd harmonics.

Any remaining dependence of the output voltage on the circuit voltage may be equalized by compensation winding 7 which is closely coupled to primary winding 2.

FIGS. 3 and 4 show a voltage regulator which has an approximately sinusoidal output voltage. The part of core 1, which according to FIG. 3 lies to the left of line AA and contains the windings 2, 3 and 7, has the same function as the corresponding above-described same numbered circuit elements of the voltage regulator having a trapezoidal output voltage.

In addition, for a voltage regulator with sinusoidal output voltage, the part on the right of line AA must be added. This consists of the winding 8 which is highly decoupled from the winding 3 by the shunt 9 and the air gap 10.

The function of this additional part is as follows:

Due to the loose coupling with winding 3 which was described above, the odd harmonics which are contained in the trapezoidal voltage are also generated in winding 8. Because of the electrical series connection of the windings 3 and 8 with the capacitor 6 (see FIG. 4), the harmonics generated in winding 8 are again present in the capacitor voltage, but in opposite phase.

By fitting the number of turns of the neutralization winding 8 to the capacitance of the capacitor, it can be accomplished that at least the low order harmonics which are mainly responsible for the departure from the sinusoidal form are approximately equal in the capacitor and coil voltage. They thus cancel each other, so that the voltage in the secondary winding and thus the output voltage of the voltage regulator is sinusoidal to a great extent. The oscillogram of FIG. 5 may serve to visualize this process. Curve 51 shows the voltage of the neutralization winding 8, curve 52 the capacitor voltage, and curve 53 is the difference voltage between the two, that is, the voltage at the secondary winding 3. Sinusoidal output voltage of the voltage regulator may be maintained in this arrangement throughout a wide range even if the input circuit voltage is not sinusoidal but is rectangular.

The magnetic decoupling by the shunt 4 between primary winding 2 and secondary winding 3, results in a further important characteristic of both voltage regulators. This concerns their short-circuit behavior. If the output of either type is short circuited, the capacitor 6 is also short circuited by transformer action and thus loses its magnetizing effect. Thus the voltage regulator characteristics is lost and in both cases a usual leakage transformer remains with which, in case of a short circuit on the load side, limits both the input current as well as the load current to a value which lies between 1.4 and 2 times the nominal values.

The above-described characteristics of the voltage regulator, namely (1) Constant output voltage independent of variations in the input voltage and independent of load variations,

(2) The short circuit behaviour, which limits both the supply and the load current, and

(3) The ability, in case of a voltage regulator having a sinusoidal output, to maintain this kind of output even when the input voltage is rectangular, indicate an extremely great commercial application for these voltage regulators, for example, in inverters. The regulation of the inverter output voltage may be saved as may be the current limiting switching elements which protect the semiconductor elements of the inverter in case of a load short circuit. If, in addition, a sinusoidal output voltage is required from the inverter, the filter may be saved, which changes the rectangular inverter voltage to a substantially sinusoidal output voltage. However, the use of voltage regulators, for example in inverters, requires several further characteristics, which are not present in the above-described conventional voltage regulators, and which form the subject of the present invention.

For example, the voltage of the battery which drives the inverter may vary over very wide ranges, namely from the final discharge voltage to that voltage which appears during a strong charging of the battery. In an un favorable case, this means a region of variation about the nominal value of -20% to +25%, in which the output voltage of the inverters is to be kept substantially constant. It is thus important to increase the regulating region of the conventional voltage regulators by suitable means.

The region of primary voltage variations within which the output voltage is to remain constant within tight limits, is limited on the high side in the described conventional voltage regulators by the increasing magnetization current of the primary winding. The primary current then increases so rapidly, that first of all, the heat generated in the winding reaches untenable values. Furthermore, the circuit elements (semi-conductors) of the inverter may be endangered if they are not considerably overdesigned. On the other hand, the control characteristics of the voltage regulators in the high region of input voltage are extremely good. An increase in the number of primary turns, that is a decrease in the magnetic induction of the input winding, would result in a decrease of the magnetization current in the over-voltage region, but on the other hand, would influence the regulatory characteristics in the low voltage region so unfavorably that an extension of the total regulatory region in this fashion is not possible. A further characteristic of the above-described voltage regulators which causes their application in inverters to be rather difficult and which also is caused by the high primary induction is the high surge current which appears when the voltage regulator is switched in, and particularly if it is switched in at the time the input voltage is passing through zero. This high surge current also endangers the semiconductor elements in the circuit.

From the theory of low loss transformers, it is well known, that the flux must reach at least double its steady state value, if the necessary counter-voltage is to be generated when the switching occurs when the supplied voltage passes through zero. If no residual flux exists, this flux becomes twice as big as the steady state flux after the passing of the transient due to the switch-in op eration. If, however, the phase of a possibly existing residual flux is unfavorable, the double value of the steady state flux may be increased by the amount of the residual flux. When one takes into consideration that the induction of conventional voltage regulators must be approximately 16 kg. at the nominal voltage for good regulatory characteristics to be achieved, it becomes apparent that the input current surge may reach maximum values which correspond to an induction of about 35 kg. This means a current surge of more than 50 times the nominal current. In order to decrease this high surge value it is of course possible to supply a series resistor or a choke, which absorbs a high percentage of the applied voltage at the moment of the switch-in operation. However, after the transient period has passed, it is then necessary to shortcircuit the resistance or choke respectively, for example, with a time switch. This means additional equipment and may result in a second transient current at the time of the short-circuiting of the series member. This second transient may also be harmful to the semi-conductors in the circuit. The just-mentioned high switchinginduction of approximately 35 kg., if the phase of the residual flux is unfavorable, and for a switching at the zero point of the applied voltage, considerably exceeds the saturation induction of the voltage regulator lamination.

SUMMARY OF THE INVENTION These drawbacks of the conventional voltage regulator are eliminated by the present invention. A considerable decrease of the current surge at the switch-in time results, if, as in accordance with this invention, a flux path is created for the absorbtion of primary leakage flux of a magnitude equal to the difference between the saturation induction of the iron which is being used and the required switching induction. According to this invention, therefore, an additional section is created in the voltage regulator which absorbs the said specified part of the primary flux.

This additional flux may be either an air flux flowing through an additional air section Q, or may be iron flux if the section Q is filled with a magnetic material, preferably of high permeability. The required ampere-turns for this additional fiux are smaller, and the current surge limiting effect larger, the smaller the median magnetic line length is. Experiments have confirmed that not only a considerable decrease in surge current, but also a considerable decrease in the steady state magnetizing current in the region of the upper circuit voltage tolerances, and thereby an extension of the regulatory region of both voltage regulator types may be effected according to this invention by the following means:

(a) Through creation of an additional section Q in which a flux may be absorbed which is coupled to the primary winding and whose magnitude compensates for the excess of the required switching induction as compared to the saturation induction of the iron that is being used;

(b) By shortening of the median line length of this addition air flux by suitable construction.

Thus this invention comprises a single core magnetic voltage regulator having a primary winding linked by primary leakage flux upon energization of said winding, and a secondary winding which is connected in parallel with a capacitance. In such a voltage regulator an additional path for said primary leakage flux is provided, thus decreasing surge currents and increasing the regulatory region.

The novel features which are considered as character istic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a single core magnetic voltage regulator having a trapezoidal output voltage;

FIG. 2 is a schematic diagram of the voltage regulator of FIG. 1;

FIG. 3 is a sectional view of a single core magnetic L voltage regulator having a sinusoidal output voltage;

FIG. 4 is a schematic diagram of a voltage regulator as shown in FIG. 3;

FIG. 5 is a oscillogram showing the neutralization coil voltage, the capacitor voltage and the difierence votlage between the two;

FIG. 6 is an end view of a voltage regulator having a coil form which is longer than the core height;

FIG. 7 is a sectional view of a voltage regulator having a primary winding wound over a compensation winding;

FIG. 8 is a sectional view of a voltage regulator as shown in FIG. 7, but with magnetic material in the leakage flux path;

FIG. 9 is a oscillogram of the primary current in an inverter voltage regulator for a 25% increase and a decrease in battery voltage, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT Conventional voltage regulators of the single core magnetic type have been described in connection with FIGS. 1 through 5. FIG. 6 shows one method for increasing the cross-sectional area in order to absorb primary leakage flux. As shown in FIG. 6, it is possible to construct a coil form 61 for the windings 2 and 7 which is larger than the height of the laminations of core 1. One thus gains an additional area 63 on both sides of the core, which is available to accommodate additional primary flux when the voltage regulator is switched in. FIG. 7 shows the flux lines of htis air flux schematically. Flux lines form in such a manner that they return to the iron by the shortest possible route. Thus, the median length of the flux lines may be represented approximately by lines 74.

FIG. 7 also shows another method of increasing the sectional area available for primary leakage flux. Here the compensation winding 7 is wound underneath, rather than on top of, the primary winding 2. Since the current surge goes only through the primary winding, the tube-like volume which is then formed between the core and the primary winding by the compensation winding furnishes room for the formation of additional air flux and thus increases the cross section Q,-

As mentioned above, shortening of the air flux line length will also tend to minimize the current surge upon switch-in. This may be accomplished by filling the increased coil form section 63 of FIG. 6 with a magnetic material having a high magnetic conductivity whose length corresponds exactly to the width 15 of the primary winding (FIG. 7). The original flux line length 74 is thereby shortened by twice the amount of the coil width 15.

A further shortening of the air flux length may be effected according to this invention by forming the magnetic material in the additional sections 63, in such a manner that, if possible, all flux lines of the original air flux are absorbed by it and returned to the main body of the core of the voltage regulator in the shortest possible way, that is the transition from the additional field in the region of the coil back to the iron core is fille-d with magnetically conducting material in the form of an are (81, FIG. 8).

The above-mentioned measures in no way worsen the regulating and short-circuit behavior of the voltage regulator. They serve simultaneously to decrease the current surge upon switch-in and to increase the regulatory region in the direction of positive battery voltage tolerances. This is verified by the oscillograms of FIG. 9. Both oscillograms show the primary current of a 250 va. voltage regulator in an inverter arrangement. Curve 91 shows the primary current for a battery voltage of 25% more than the nominal voltage, while curve 92 shows the primary current for a battery voltage whose value is 20% less than the nominal value. The magnetizing peaks which are readily visible at the overvoltages do not exceed the peak value of the regulator current at minimum battery voltage. This is caused solely by the applications of the measures of the present invention. A conventional voltage regulator has a steady state magnetization current peak for a 25 overvoltage which is at least 5 times as great as the crest value present at a 20% decrease in nominal voltage.

The switch-in current surge, which for a conventional voltage regulator, operated at nominal voltage, may reach more than times the steady state value (when switching takes place during the time voltage passes through zero), is held to approximately 2 /2 times the steady state value under the same conditions by the application of the system according to this invention.

This relatively small current surge may then be decreased by means of a suitable inverter input filter so that an overdesign of the semiconductor elements becomes superfluous.

It should be further noted that a sinusoidal output voltage of a voltage regulator according to this invention in which the battery voltage may vary from +25% to 20% at full load may be kept constant to a value of i2% of the nominal voltage. In connection with this, it should further be noted that the voltage variations at the input of the voltage regulator, due to the unavoidable voltage drops in the inverter circuit elements (chokes, semiconductors) considerably exceed the above-specified voltage variations of the battery.

When connected to a current source, the same voltage regulator, for an input voltage variation of +25% to -20% exhibits an even better output voltage stability, namely il%. The above-described arrangements according to this invention do not only have great utility for the use with inverters, but, also as line voltage regulators. Their use is always an advantage when the regulatory region of conventional voltage regulators of :15 of the line voltage is insufficient. The decrease of current surge upon switch-in that results from use of a voltage regulator according to the present invention may also be a decisive advantage for its use as a line operated voltage regulator.

While the invention has been illustrated and described as embodied in voltage regulators, wherein additional flux paths and shortening of the flux lines is provided in particular constructions, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can be applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this inven tion and, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A magnetic voltage regulator having a load, comprising, in combination, a single core; a compensation Winding connected in series with said load, said compensation winding being wound relative to said core in such a manner that an air gap path is created between the external surface of said core and the internal surface of said compensation winding; a primary winding linked by primary flux upon energization, said primary winding being wound over said compensation winding; a secondary winding wound on said core; and a capacitance in parallel with said secondary Winding.

2. A magnetic voltage regulator as set forth in claim 1, wherein said air gap is filled with magnetic material.

3. A magnetic voltage regulator as set forth in claim 2, wherein said magnetic material has a shape corresponding to the shape of the flux lines.

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